Electrically amplified musical instruments having pickups and sustain-inducing drivers typically operate in the following manner: The pickup provides a feedback signal representative of the vibration of the vibratory element (such as a string or a head of a percussion instrument). The amplifier accepts the feedback signal from the pickup and provides a drive signal to the driver. The driver accepts the drive signal and provides a drive force to the vibratory element that sustains the vibration of the vibratory element.
The most common musical instrument of this type is a stringed musical instrument such as a guitar, which includes a plurality of magnetically permeable strings. Vibration of a string disturbs the magnetic field associated with the pickup. The pickup provides a feedback signal representative of the string vibration. The amplifier boosts the current and voltage of the feedback signal to provide a drive signal. The drive signal is then applied to the driver. The drive signal causes a disturbance in the magnetic field emitted by the driver which applies a drive force to the string. This drive force emitted by the driver comprises a magnetic field that impinges upon the string. The drive force reinforces the string vibration thereby sustaining the string vibration. An example of an electrified, stringed musical instrument for which the present invention is especially well adapted is the Fender STRATOCASTER guitar, and various STRATOCASTER copies referred to as "Strats".
Prior art electric guitars generally comprise a structure having a body portion and a neck portion coupled to, and extending away from the body portion. A plurality of strings are supported by the body portion and neck portion. A bridge is provided on the body to support one end of each string. A bridge pickup is disposed underneath the strings in close proximity to the bridge. The bridge pickup provides a signal representative of string vibration near the bridge. The bridge pickup signal emphasizes the higher harmonic frequencies of the vibrating strings because the bridge pickup is located near one end of the strings. A neck pickup is disposed underneath the strings at a location remote from the ends of the strings. The neck pickup provides a signal representative of string vibration remote from the ends of the strings. The neck pickup signal emphasizes the fundamental frequencies of the vibrating strings because the neck pickup is located remote from the ends of the strings.
Some models of known instruments provide a middle pickup disposed underneath the strings, and positioned between the bridge pickup and the neck pickup. Because of its positioning, the middle pickup provides a signal representative of string vibration between the bridge pickup and neck pickup. The middle pickup signal provides a balanced mix of fundamental frequencies and higher harmonic frequencies of the vibrating strings. From a musically artistic aspect, it is generally accepted that the bridge pickup and neck pickup are of greater importance than the middle pickup, as demonstrated by the fact that some popular electric guitar models do not provide any middle pickup.
Numerous designs of prior art pickups have evolved over the past 40 years to be highly optimized for their intended artistic uses. One of the challenges involved in the design of a driver is to make it compatible with existing pickups. For example, one prior art multi-string driver is the GA-2 driver manufactured by Audio Sound International, Inc. This driver is disposed underneath the strings at the neck pickup position. In the GA-2 sustainer, the bridge pickup provides the feedback signal to the amplifier. This arrangement provides a relatively long distance between the driver and the bridge pickup to decrease the effects of direct magnetic feedback on the pickup. However, one disadvantage with this arrangement is that it replaces the highly-optimized prior art neck pickup with a driver. To overcome this disadvantage, the driver of the present invention is disposed underneath the strings between the neck pickup and the bridge pickup. The driver is not disposed in close proximity to either the bridge pickup or the neck pickup to thereby decrease the shifting of the intersection between the strings and the magnetic fields emitting from the pickups. The driver of the present invention emits a narrowly dispersed lateral magnetic field to further decrease shifting of the intersection.
A typical prior art pickup emits a magnetic field from its core that impinges on the strings. The pickup's magnetic field has a predetermined three dimensional shape that is governed by the geometry of the pickup's magnetic core. The intersection between the pickup's magnetic field and the strings provides the characteristic tonality of the pickup. Since different string harmonic frequencies have nodal points at different points along the string, the length and location of intersection determines the pickup's sensitivity to the different harmonics.
When a driver is place in proximity to the pickup, the nature (e.g., length and location) of the intersection is changed due to the shifting force between the magnetic field of the pickup and the magnetic field of the driver. This interaction occurs because the magnetic field emitting from the driver applies a shifting force that repels a like-polarity magnetic field emitting from the pickup, thereby shifting the shapes and locations of the driver's magnetic field and the pickup's magnetic field. Likewise, the magnetic field emitting from the driver applies a force that attracts an opposite-polarity magnetic field emitting from the pickup also causing shifting.
The shifting force shifts the predetermined shape of the magnetic fields emitted by the driver and the pickups, and adversely affects the characteristic tonality of the bridge pickup and the neck pickup, thereby diminishing the artistic expression. For example, if the magnetic field associated with the bridge pickup is repelled away from the driver in the direction of the bridge, the flux density directly above the bridge pickup, will be less than it would have been had the shifting force not been present. Furthermore, the flux density will be greater between the bridge pickup and the bridge because the driver's magnetic field shifts the bridge pickup's magnetic field toward the bridge. Such a shift in the flux density causes a shift in the intersection between the pickup's magnetic field and the strings. Due to this shift, the bridge pickup will have a greater response to string vibration nearer the bridge than it otherwise would have had. Therefore, since string vibration nearer the bridge is richer in harmonic frequencies, the shifting force produces a tonality from the bridge pickup that will be subjectively "brighter".
It is therefore one objective of the present invention to provide a musical instrument, and a sustainer for a musical instrument that overcomes these problems with shifting forces that are present in some known prior art devices and that are worsened when the driver is placed between the neck pickup and the bridge pickup.